All, Like the title states, how clean does the metal need to be for gray epoxy? Is this good enough? or does it need to be bare-bare....clean? Thanks!
The great thing about sandblasting is it gets the rust out of the pits. Sandpaper just rides on the surface. Why would you do the job halfway? It seems you blasted the rust off the surface, but left it in the pits.
That's like asking a surgeon, how sterile does the knife need to be to perform the operation? Failure to clean the rust will just mean you left behind the cancer you were hoping to remove.
Sandblasting sheetmetal is pretty risky to begin with as it may warp the panel On the larger panels, you might want to buy a surface conditioning tool and some rollers. There are lots of different prices and shapes. I bought an Eastwood because I like its design even tho it costs more than some of the cheap ones. You also have to look at the prices of the wheels they sell. I bought some replacement stripping wheels off Amazon, and found they fit the Eastwood just fine and were much cheaper. As for the thicker metal pieces, I'd just run em thru the sandblaster till all the rust is gone. That finish may be ok for some type of equipment that you are going to put tractor paint on, but I wouldn't try to use it in a car paint job. https://www.google.com/search?q=sur...57j0i512l9.9085j0j15&sourceid=chrome&ie=UTF-8
Rust is a living organism, and needs two things to grow-ferrous metal and oxygen, and can be removed mechanically (sandblasting or sanding) or chemically (etch primer, 25% vinegar solution. or other chemicals). You could blast it some more, sand it, or treat it.
Head down to your local hardware store and buy either Ospho, or Jasco Prep and Primer (reasonable functional equivalents), and some rubber gloves. Brand depends on store and marketing region. Apply as directed on the container. Allow to dry.
Ospho is a great option...stops and or converts the rust..not always easy or situation permits all that sand dust.....
Do not use ospho on blasted steel. On small yhings and outer panels its ok, on the inside of a cab or door framework, and places with lots of detail and lap joints, nononono. when you blast steel, its meant to be perfectly clean, cleaner than you have (see that pic posted after yours), epoxied right away and not need ospho. 80 gritting it after blasting is a waste of time, its already keyed by the blasting material., again the exception of sanding the outside of panels and small easy to get to stuff obviously Do not use them green wash primers on blasted metal, for one it sinks off the peaks and falls in the pits, for two it needs a surfacer over it, so youve now just wasted double the time, money and product over using epoxy. Sand blasting warping panels is a blatant lie. No one here needs to worry about that with the blasters and material theyre using, and, any professional blasting company worth its salt will know exactly what they can get away with, without warping it... The two ingredients to make rust are actually moisture and air with metal. you DO NOT want to ospho and leave a car with it dried on the ‘seal it from rust while its metal worked’ either.. You epoxy it after blasting. Sanders still remove epoxy to metal work zones.. you blast and epoxy. Done. You never haveto go over the inside of the body ever again. If anyone insists on using the green stuff, sealing it, sanding the sealer, painting it etc theyre shafting you and riding the clock. If you insist in doing that, dont sand it to get the ospho off, the phosphoric acid dust will destroy your lungs no matter how sterile you are with it, you cant get away from it.. Dont ospho the inside of the cab, youll have to wet it with ospho to get it off (like attracts like) which means water will all get in your crevices.. Youll never get all thd white powder oug of sll the crevices and joins.. Blast. Epoxy it immediately. save up, have a company blast it, save a little big more so thry can epoxy it for you. Spend the hours youre saving at the beach, or earning money. Theres plenty more you can do to get your hands dirty.
When you metal condition blasted steel, it sinks into the pits, youll never get it properly out snd itll dry powdery.. and when you try wipe on and eipe off, youll leave so much lint all through the sharp steel blasted surface youll invent a few new naughty words
I agree with chev54. Most modern epoxys do not want metal etch, after blast or anything like that under the epoxy. But to be safe always read the spec sheet on the material you use. There’s a lot of info in them. I do disagree though a sand blaster can warp some panels quickly. Even the so called hood ones. Even if there using the water mix with bead. It’s not always the heat that warps them. I do prefer sandblasting and I always go over the body panels with 80 grit. It will help to grab some of the material left behind from blasting and pull it out. and yes it needs to be clean. Do it once. Remember if you jack up the first step in painting the other steps are screwed also.
That’s about what mine looked like after I blasted it. I blasted, did weld repairs, added body filler where needed to the bare metal, then applied epoxy primer. After that, primer surfacer, block sanding, etc before a seal coat of epoxy primer and single stage urethane. That was 3 years ago. Paint hasn’t fallen off yet. I know there’s some controversy about “what’s right,” and I’m not claiming I did it right, but it has worked for me so far.
I think warping sheet metal is having the large portable compressors , I used to have one as I recall it was 180psi and 100+ cfm. Diesel driven with no tank. I think you have less chance of damages with home shop compressor and blaster. I might be off base, just my thinking.
Looks like the OP may have used a siphon blaster or cheap HF pressure blaster. Both of which are inadequate. I stepped up to a 'Texas Blaster'. Not commercial quality but does a pretty good job. Bigger hose, much better nozzle, etc. Your metal needs to look something like this. Need to get all the rust out of the pits. Also, panel warpage isn't really an issue with the small home DIY units. I think 54chevkiwi is right on the money with his analysis.
You can make the POS harbor blaster work. I pressure the tank to 10-20lbs. Then use a separate hose to run a siphon gun. Works extremely well
The blasting material is also peening the metal which can cause warp. My last guy ran 80psi on a diesel compressor to blast with. But I wouldn’t let him touch the roof or the hood. Those get air tools to strip. Just my 2cents
Interesting. Any way you can explain how I have managed to have flawless results doing this over the last 45-ish years, on over 100 builds? I guess I must have impeccable luck. I guess I must also be dead by now, too!
Funny, when I read that comment I was just getting ready to put Ospho on yet another part. I took a quick break and called my uncle, to inform him that more than likely both he and I are dead by now. And that the method that his father, my grandfather taught us to do things is in fact invalid, and doesn't work. I had him check on the model A that I did for him in 1982, and on the 1946 John Deere Series H tractor that I restored and gave to him in 1995, to see if there was any signs of paint failure. He says there weren't, and he's not nice to either one of them. Both get used and driven. So if y'all excuse me, I need to go play the lottery, and go see if I can turn some water into wine.
Just to counterbalance mis-information here. I always 80 grit DA a sandblasted surface. Why? To remove any stray bits of sand, stuck in the pores, and to smooth out the metal a bit. I also use "acids" (metal prep, Ospho, phosphoric) over large areas, and let them sit . Yeah, I work on VERY rusty cars sometimes! A lot of times overnight, covered with a layer of plastic wrap, so it doesn't evaporate. Next day, wire brush, and inspect. If there is still dark spots in the pits, repeat. In the end, be sure to wash the area with fresh acid, then water wash to neutralize, blow dry and wipe with alcohol. ALWAYS remove any residue from acid, with a fresh acid wash and then rinse with water, to neutralize/dilute. Then quickly dry to prevent flash rust.
I buy boxes containing 4 1-gallon bottles of 99% isopropyl alcohol often enough that I am probably on in some suspicious activities database.
The Jalopy Journal
